Examples of background art of the present field include JP 2011-247192 A. In this publication, in a booster circuit of a fuel injection system, the number of times of boost switching until restoration to a set voltage after a booster capacitor discharges is measured; and, when the criteria of a set number of times of switching is exceeded, drive of a fuel injection valve is permitted. It is not an object of this publication to carry out deterioration judgment, but is to wait for recovery of the capacitor having lowered capability in initial usage and restart operation of the booster circuit.
Moreover, examples of background art of the present field also include JP 2011-247192 A. In this publication, in a booster circuit of a fuel injection system, a steady-state value of a charge voltage for a booster capacitor is monitored. If it is normal, a fuel injection valve is driven by a control signal indicating a normal injection pulse width and injection timing; and, if it is not normal, the injection pulse width and injection timing are corrected. In this publication, the stead-state value is monitored for the charge voltage for the booster capacitor. However, since no change is generated in the steady-state value, it is difficult to detect the deterioration of the booster capacitor.